U.S. patent application number 10/904163 was filed with the patent office on 2005-07-07 for oil contaminated substrate treatment method and apparatus.
This patent application is currently assigned to RACIONAL ENERGY AND ENVIRONMENT COMPANY. Invention is credited to Cordova, Ramon Perez.
Application Number | 20050145418 10/904163 |
Document ID | / |
Family ID | 34590070 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050145418 |
Kind Code |
A1 |
Cordova, Ramon Perez |
July 7, 2005 |
OIL CONTAMINATED SUBSTRATE TREATMENT METHOD AND APPARATUS
Abstract
A method and apparatus for treating for disposal oil
contaminated substrates, such as drill cuttings from drilling with
an oil-based mud, by steam distillation. If necessary, the
contaminated substrate 10 can be pretreated with an emulsion
breaker 14. The contaminated substrate 10 can be treated with steam
16 in a first mixing still 12. The substrate can be optionally
treated with a second steam source 20 in a second mixing still 18.
The steam provides heat to vaporize the oil, moisture to treat the
substrate and water to the reaction mixture. Recoverable
constituents in the vapor can be condensed in a vapor collection
system 24. The treated substrate 22 is essentially free of oil and
can have a controlled water content. The process exhibits low
energy consumption, rapid treatment, compact equipment and a high
degree of process control.
Inventors: |
Cordova, Ramon Perez;
(Lerma, MX) |
Correspondence
Address: |
LUNDEEN & DICKINSON, LLP
PO BOX 131144
HOUSTON
TX
77219-1144
US
|
Assignee: |
RACIONAL ENERGY AND ENVIRONMENT
COMPANY
6100 Nell Rd., Suite 500
Reno
NV
|
Family ID: |
34590070 |
Appl. No.: |
10/904163 |
Filed: |
October 27, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60481611 |
Nov 7, 2003 |
|
|
|
Current U.S.
Class: |
175/66 ; 196/123;
196/126; 196/127; 208/188 |
Current CPC
Class: |
E21B 21/066 20130101;
B09C 1/06 20130101; B09B 3/00 20130101; B01D 3/38 20130101; C10G
1/02 20130101; B09B 3/0083 20130101 |
Class at
Publication: |
175/066 ;
208/188; 196/123; 196/126; 196/127 |
International
Class: |
C09K 007/00; C10G
033/04; C10G 007/00 |
Claims
What is claimed is:
1. A steam distillation method for removing hydrocarbons from a
substrate comprising oil contaminants, the method comprising: (a)
pretreating the substrate with an organic emulsion breaker; (b)
heating the pretreated substrate with a heat transfer medium to
vaporize the oil; (c) recovering the vaporized oil; (d) recovering
a treated substrate of reduced oil content.
2. The method of claim 1, wherein the substrate heating comprises
direct heat transfer.
3. The method of claim 1, further comprising admixing the heat
transfer medium with the substrate.
4. The method of claim 1, wherein the heat transfer medium
comprises steam.
5. The method of claim 1, wherein the heat transfer medium
comprises air or nitrogen.
6. The method of claim 3, further comprising fluidizing the
substrate.
7. A steam distillation method for removing hydrocarbons from a
substrate comprising oil contaminants, the method comprising:
admixing the substrate with a first steam source with vigorous
mixing to vaporize the oil therein; recovering steam vaporized oil;
and recovering a treated substrate of reduced oil content.
8. The method of claim 7, wherein the substrate comprises drill
cuttings.
9. The method of claim 7, wherein the substrate contains less than
10 percent oil by weight.
10. The method of claim 7, further comprising pretreating the
substrate with an organic emulsion breaker prior to the admixing in
(a).
11. The method of claim 10, wherein the emulsion breaker comprises
an organic acid or addition salt.
12. The method of claim 11, wherein the emulsion breaker comprises
alkylsulfonic acid, arylsulfonic acid, alkylarylsulfonic acid,
aralkylsulfonic acid, or a combination thereof.
13. The method of claim 10, wherein the emulsion breaker comprises
alkylbenzenesulfonic acid.
14. The method of claim 10, wherein the emulsion breaker comprises
dodecylbenzenesulfonic acid.
15. The method of claim 7, further comprising admixing the treated
substrate from (a) with a second steam source with agitation to
further vaporize remaining oil, and recovering a solid product
essentially free of oil.
16. The method of claim 7, wherein the admixing in (a) is under
high shear conditions.
17. The method of claim 7, wherein the substrate is fluidized.
18. The method of claim 7, further comprising: continuously
introducing the substrate into an inlet end of a first mixing still
comprising at least one rotatable shaft disposed longitudinally in
a housing and having a plurality of impellors spaced along the
shaft; if the substrate has a water content of less than 20 weight
percent or an oil content of more than 30 weight percent,
continuously introducing an organic emulsion breaker into the first
mixing still at a first location adjacent the inlet end;
continuously introducing a first steam source into the first mixing
still at a second location adjacent to an outlet end of the first
mixing still; rotating the at least one shaft of the first mixing
still to continuously maintain high shear conditions in the first
mixing still and discharge the treated solid substrate essentially
free of oil.
19. The method of claim 18, wherein the substrate has a residence
time in the first mixing still of less than 100 seconds.
20. The method of claim 18, wherein the substrate has a residence
time in the first mixing still of less than 50 seconds.
21. The method of claim 18, wherein the substrate is fluidized in
the mixing still.
22. The method of claim 18, wherein the substrate comprises drill
cuttings.
23. The method of claim 22, wherein the drill cuttings comprise oil
contaminated clay.
24. The method of claim 22, wherein the drill cuttings are
contaminated with oil-based drilling mud.
25. The method of claim 22, wherein the substrate contains less
than 10 percent oil by weight.
26. The method of claim 18, further comprising pretreating the
substrate with an organic emulsion breaker prior to the admixing in
(a).
27. The method of claim 26, wherein the emulsion breaker comprises
an organic acid or addition salt.
28. The method of claim 27, wherein the organic acid or addition
salt comprises alkylsulfonic acid, arylsulfonic acid,
alkylarylsulfonic acid, aralkylsulfonic acid, or a combination
thereof.
29. The method of claim 26, wherein the emulsion breaker comprises
alkylbenzenesulfonic acid.
30. The method of claim 26, wherein the emulsion breaker comprises
dodecylbenzenesulfonic acid.
31. The method of claim 26, wherein the emulsion breaker is admixed
at a rate of from 0.5 to 5 parts by weight per 100 parts of
substrate.
32. The method of claim 18, further comprising recovering vapor
generated from the first mixing still, condensing the recovered
vapor and exhausting non-condensed gases.
33. The method of claim 18, further comprising: continuously
introducing the treated solid substrate from the first mixing still
into an inlet end of a second mixing still comprising at least one
shaft disposed longitudinally in a housing and having a plurality
of impellors spaced along the shaft; continuously introducing a
second steam source into the second mixing still at a location
adjacent an outlet end thereof; rotating the at least one shaft of
the second mixing still to maintain high shear conditions in the
second mixing still and continuously discharge a solid substrate
from the outlet end of the second mixing still, wherein the solid
substrate is essentially free of oil.
34. The method of claim 18, further comprising peptizing the
substrate with alkaline earth.
35. The method of claim 34, wherein the alkaline earth comprises
lime.
36. The method of claim 34, wherein the alkaline earth is added to
the substrate prior to being introduced into the first mixing
still.
37. The method of claim 18, further comprising peptizing the
substrate with mineral acid.
38. The method of claim 18, wherein the emulsion breaker is admixed
at a rate of from 1 to 1.5 parts by weight per 100 parts of drill
cuttings.
39. The method of claim 33, further comprising recovering vapor
generated from the first and second mixing stills, scrubbing the
recovered vapor and exhausting non-condensed gases from the
recovered vapor into the atmosphere.
40. The method of claim 39, wherein the vapor exits the mixing
still through insulated columns connected to a condensing
column.
41. The method of claim 39, wherein the water is recovered by
condensation is recycled to the steam supply.
42. The method of claim 33 wherein the substrate in the second
mixing still is fluidized.
43. A method for treating drill cuttings contaminated with oil,
comprising: continuously introducing the drill cuttings into an
inlet end of a first mixing still comprising at least one rotatable
shaft disposed longitudinally in a housing and having a plurality
of impellors spaced along the shaft; continuously introducing a
first steam source into the first mixing still from a location
adjacent an outlet end thereof; rotating the at least one shaft of
the first mixing still to continuously maintain high shear
conditions in the first mixing still and discharge an intermediate
solid substrate; continuously introducing the intermediate solid
substrate into an inlet end of a second mixing still comprising at
least one shaft disposed longitudinally in a housing and having a
plurality of impellors spaced along the shaft; continuously
introducing a second steam source into the second mixing still at a
location adjacent an outlet end thereof; rotating the at least one
shaft of the second mixing still to maintain high shear conditions
in the second mixing still and continuously discharge a solid
substrate from the outlet end of the second mixing still, wherein
the solid substrate contains less than 3000 ppm oil; recovering
vapor from the first and second mixing stills; condensing liquid
from the recovered vapor to form an exhaust stream of uncondensed
vapor.
44. The method of claim 43 wherein the impellers on the first and
the second mixing still shafts are rotated at between 2 and 8
meters per second.
45. An apparatus for the treatment of an oil contaminated substrate
comprising: means for admixing the substrate with steam and
agitation to vaporize the oil therein; means for recovering steam
vaporized oil from the admixing means; and means for recovering a
treated substrate of reduced oil content from the admixing
means.
46. An apparatus for the treatment of an oil contaminated
substrate, the apparatus comprising: means for pretreating the
substrate with an organic emulsion breaker; means for heating the
pretreated substrate with a heat transfer medium to vaporize the
oil; means for recovering the vaporized oil from the heating means;
and means for recovering a treated substrate of reduced oil content
from the heating means.
47. An apparatus for the treatment of an oil contaminated
substrate, comprising: a first reactor comprising a longitudinal
housing having an inlet at a first end and an outlet at an opposite
end, the first reactor having at least one rotatable shaft disposed
longitudinally in the housing, and having a plurality of impellers
spaced along the at least one shaft; a second reactor comprising a
longitudinal housing having an inlet at a first end and an outlet
at an opposite end, the second reactor having at least one
rotatable shaft disposed longitudinally in the housing, and having
a plurality of impellers spaced along the at least one shaft; a
steam source for continuously introducing steam into the first
reactor at a location adjacent an outlet of the first reactor and
into the second reactor at a location adjacent an outlet of the
second reactor; a first feeder for continuously introducing the
substrate into the inlet of the first reactor; a chute for
continuously transferring reaction product from the outlet of the
first reactor into the inlet of the second reactor; a second chute
for continuously removing reaction product away from an outlet of
the second reactor; a vapor collection system for recovering gases
from the first and second reactors; a condenser for condensing
liquid from the gases from the vapor collection system and
producing a stream of uncondensed gases; and an exhaust port for
discharging uncondensed gases.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to U.S. Provisional
Application Ser. No. 60/481,611 filed in the United States Patent
and Trademark Office on Nov. 7, 2003.
FIELD OF THE INVENTION
[0002] This invention relates to the thermal treatment of solid
substrates contaminated with oil for the environmentally acceptable
disposal, and more particularly to the treatment of the drill
cuttings with steam, and an optional organic demulsifier, for the
purpose of rapidly removing oil from the drill cuttings to obtain
treated drill cuttings essentially free of oil.
[0003] Oil-based drill cuttings are generally regarded as
controlled or hazardous waste. As such, the drill cuttings can be
disposed of in two different ways: (1) decontamination treatment;
or (2) hazardous waste controlled landfill. Hazardous waste is
considered a threat to the environment due to the risk of surface
and subsurface water pollution, air pollution, and interrupting the
equilibrium of the ecosystem. The disposal of hazardous waste in
controlled landfills is usually a last environmental option, since
the problem is only transferred from one place to another, and the
ultimate solution and need for decontamination is merely postponed
to a later date.
[0004] There are several technologies available to treat hazardous
wastes. Each has advantages and limitations depending upon the
concentration and type of contaminant, the matrix in which the
contaminant is dispersed, and the locations at which the cuttings
are generated and are to be disposed of, which can be the same or
different. The handling and treatment costs, process time,
contaminant locations, such as for example, ecologically protected
areas, nearby water bodies, human residences, deserts, to name a
few, and finally the total treatment time, are all factors
considered in selecting the best available technology.
[0005] Oil and gas exploration depends on drilling wells at
different depths with different diameters throughout different
geological strata having multiple lithological manifestations such
as clay, rock, sand, empty underground salt mines, brine and water
tables. Drilling requires a drilling fluid, also known as drilling
mud, having various physical functions such as: (1) cooling and
lubrication of the drill bit; (2) formation of a filter cake for
temporarily `casing` the wellbore; (3) carrying the drill cuttings
from the bit to the surface; and (4) preventing blowout of
reservoir fluids. The solid pieces of material cut by the bit, as
the drilling advances, are known as drill cuttings. The drilling
mud is a fluid of physical-chemical compounds with specific
rheological characteristics to cover all the needs of the well as
the different geological layers, depths and extreme pressure of
natural fluids are met.
[0006] There are two principal types of mud: (1) oil-based mud
(also known as inverse emulsion mud); and (2) water-based mud.
Their formulations vary according to the technology of each
supplier and the general characteristics of each well in each
field. These formulations are generally expensive, which is the
reason for recirculating them. Before recirculation, their
formulation must be adjusted to replace compounds lost during the
process. The composition of many drilling muds typically includes
the following compounds: (1) bentonite; (2) barite; (3) diesel or
other oil; (4) polymers; (5) sodium, calcium and potassium
chlorides; (6) lime; and (7) water. Water-based mud does not use
diesel or oil, but does use the chlorides. The inverse emulsion
generally uses more diesel than water, and may also include
hydrocarbons to enhance the lubricating properties of the fluid. As
used herein, the term "oil-based mud" also includes synthetic muds
that are sometimes classified separately even though they contain
appreciable amounts of hydrocarbons. Oil-based mud typically can
include refined hydrocarbons instead of diesel. Even though
oil-based muds can be cheaper to use and can have operating
advantages, water-based mud is sometimes used instead of the
oil-based drilling fluids because the water-based mud has fewer
issues related to disposal.
[0007] In all cases, the mud is a stable physical emulsion,
necessarily so to prevent separation of its components that may
have different densities and other physical-electrical
characteristics. Mud can be sticky and elastic, like gum, without
losing its fluid qualities. As the contaminated oil-based drill
cuttings lose water, they become stickier in nature.
[0008] The mud is injected through the center of the drill string
to the bit and exits to the surface in the annulus between the
drill string and the wellbore, fulfilling, in this manner, the
cooling functions and lubrication of the bit, casing of the well
and, finally, carrying the drill cuttings to the surface. At the
surface, the mud can be separated from the drill cuttings to be
reused, and the drill cuttings can be disposed of, usually in
controlled landfills.
[0009] The separation of the mud and drill cuttings is not perfect
since the cuttings retain part of the drilling mud in
concentrations that can vary between 25 and 50 weight percent, or
greater. Thus, drill cuttings can be considered hazardous waste,
depending on the residual components of the mud and their
concentrations. Because of the presence of hazardous compounds such
as diesel, chlorides, polymers, etc., environmental concerns demand
that the drill cuttings showing contaminant characteristics be
handled and processed carefully before disposal into the
environment. Several known prior art technologies for the treatment
of inverse emulsion contaminated drill cuttings include: (1)
incineration; (2) stabilization and encapsulation; (3) thermal
desorption; (4) chemical oxidation; (5) biochemical degradation;
and (6) controlled landfills. The criteria used most often for
selecting the best technology are: (1) environmental reliability
(environmental risk); (2) specific environmental requirements, by
legislation as well as geographical location; (3) limitations
presented by each technology (reliability of the equipment and
processes); (4) costs; (5) process speed vs. cuttings generation
speed; (6) available space for treatment; (7) characteristics of
the final disposal site; and (8) logistics. Encapsulation is rarely
used because of the high risks involved since there is no guarantee
of 100% encapsulation nor is there a guarantee that encapsulation
will last over a long period of time under any environment at the
final disposal site. Examples of encapsulation are disclosed in
U.S. Pat. No. 4,913,586 to Gabbita; and U.S. Pat. No. 5,630,785 to
Pridemore et al.
[0010] Biochemical degradation, as disclosed in U.S. Pat. No.
5,039,415 to Smith, requires constant supervision and control
during the entire process, and this option is time consuming and
treatment may take several years in each case. Controlled landfill
is less and less attractive since the problem is not solved, and
only changes the place and time for ultimate resolution.
Additionally, this method of treatment may not be attractive for
offshore drilling applications.
[0011] Examples of incineration processes include U.S. Pat. No.
1,444,794 to Kernan; and U.S. Pat. No. 4,606,283 to DesOrmeaux et
al. The main limitation for incineration lies in the operational
costs and process control difficulties due to tight stoichiometric
operating ranges that are hard to maintain when contaminant
concentrations are variable. Moreover, the incineration process is
energy intensive because the entire matrix has to be heated to
combustion temperatures, and many of the constituents have high
thermal coefficients. Furthermore, flexibility to set up
incineration equipment in the field is low and the logistical costs
are high.
[0012] Thermal desorption, as disclosed in U.S. Pat. No. 5,228,804
to Balch, U.S. Pat. No. 5,272,833 to Prill et al. and U.S. Pat. No.
5,927,970 to Pate et al., presents several limitations, including
low thermal efficiency, poor process control, low flexibility, high
investment and operating costs, and low feasibility for in situ
projects. The thermal efficiency of thermal desorption process is
even lower than for incineration since the entire matrix is exposed
to indirect heating, creating additional investment, maintenance
and operational costs, along with poor process control. The
viscoelastic characteristics of drill cuttings make processing
difficult because of a tendency for the drill cuttings to stick to
walls and other equipment surfaces, thereby reducing thermal
transmission by effectively decreasing the inner diameter of the
drum with less productivity and/or quality. Furthermore, thermal
desorption requires additional treatment for the recovered gases,
by condensation or other means of treatment, further increasing the
cost.
[0013] Prill et al. disclose supplying indirect heat to hydrocarbon
materials and combusting the hydrocarbons and other combustibles at
temperatures between 371.degree. and 427.degree. C. (700.degree.
and 800.degree. F.). Balch discloses recovering hydrocarbon
contaminants from contaminated soil through the injection of heated
air into an ex situ body to vaporize volatile hydrocarbons.
[0014] There are several patents disclosing rotary kilns designed
to remove volatile hydrocarbons and other contaminants from solids,
such as for example, drill cuttings or sludge. Representative
references include U.S. Pat. Nos. 5,152,233; 5,199,354; 5,302,118;
and 5,378,059. Rotary kilns generally provide indirect heat to
drive volatile hydrocarbons absorbed on solids for disposal.
[0015] The recovery of oil from refinery sludges by steam
distillation is disclosed in U.S. Pat. No. 4,014,780 to McCoy.
Specifically, sludge materials are passed downwardly through a
series of rotating gates where the materials are contacted with
steam. The steam vaporizes volatile hydrocarbons contained within
the sludge and/or substrate as the vapor rises within the
chamber.
[0016] Chemical oxidation is disclosed in U.S. Pat. No. 5,414,207
to Ritter, for example. In this approach, lime preconditioned with
a hydrophobizing agent is blended with wet soil in an inert
atmosphere and introduced to a decomposition vessel. Air can be
introduced to the mixture to effect oxidation and/or hydrolysis of
the oil contaminants. The main focus of this approach is to delay
hydrolysis of the lime until well after the mixture is blended to
favor oxidation/hydrolysis of the organic contaminants, and as a
consequence the process is relatively slow and not continuous.
SUMMARY OF THE INVENTION
[0017] The present invention is directed to the discovery of a
distillation method and apparatus for treating a substrate
contaminated with oil for environmental disposal. Where desired,
the process provides for the pretreatment of the substrate with an
emulsion breaker, mineral acid, and/or alkaline earth, followed by
the addition of steam or some other direct heat source, under
conditions of vigorous agitation, preferably high shear. The
present invention achieves rapid contaminant removal with residence
times of 100-120 second or less.
[0018] In a first embodiment of the present invention is provided a
distillation method for removing hydrocarbons from a substrate
comprising oil contaminants. The method includes the steps of: (a)
pre-treating the substrate with an organic emulsion breaker; (b)
heating the pretreated substrate with a heat transfer medium to
vaporize the oil; (c) recovering the vaporized oil; and (d)
recovering a treated substrate of reduced oil content.
[0019] The substrate heating can be done by direct heat transfer.
The method can include admixing the heat transfer medium with the
substrate. The heat transfer medium can be steam, air or nitrogen.
The substrate can be fluidized.
[0020] In another embodiment of the invention, a steam distillation
method for removing hydrocarbons from a substrate comprising oil
contaminants is provided. The method can include the steps of: (a)
admixing the substrate with a first steam source with vigorous
mixing to vaporize the oil therein; (b) recovering steam vaporized
oil; and (c) recovering a treated substrate of reduced oil
content.
[0021] The substrate can include drill cuttings, and the substrate
can contain less than 10 percent oil by weight. The method can also
include pre-treating the substrate with an organic emulsion breaker
prior to the admixing in (a). The emulsion breaker can include an
organic acid or addition salt. The emulsion breaker can include an
alkylsulfonic acid, arylsulfonic acid, alkylarylsulfonic acid,
aralkylsulfonic acid, or a combination thereof. The emulsion
breaker can include alkylbenzenesulfonic acid or
dodecylbenzenesulfonic acid. The method can further include
admixing the treated substrate from (a) with a second steam source
with agitation to further vaporize remaining oil, and recovering a
solid product essentially free of oil. The admixing can be under
high shear conditions, and the substrate can be fluidized.
[0022] The method can further include the steps of: continuously
introducing the substrate into an inlet end of a first mixing still
comprising at least one rotatable shaft disposed longitudinally in
a housing and having a plurality of impellors spaced along the
shaft. If the substrate has a water content of less than 20 weight
percent or an oil content of more than 30 weight percent, an
organic emulsion breaker can be continuously introduced into the
first mixing still at a first location adjacent the inlet end, and
a first steam source can be continuously introduced into the first
mixing still at a second location adjacent to an outlet end of the
first mixing still. The at least one shaft of the first mixing
still is rotated to continuously maintain high shear conditions in
the first mixing still and discharge the treated solid substrate
essentially free of oil.
[0023] The substrate can have a residence time in the first mixing
still of less than 100 seconds. The substrate can have a residence
time in the first mixing still of less than 50 seconds. The
substrate can be fluidized in the first mixing still and can
include drill cuttings. The drill cuttings can include oil
contaminated clay or can be contaminated with oil-based drilling
mud. The substrate can contain less than 10 percent oil by
weight.
[0024] The method can further include pre-treating the substrate
with an organic emulsion breaker prior to the admixing. The
emulsion breaker can include an organic acid or addition salt,
which can include an alkylsulfonic acid, arylsulfonic acid,
alkylarylsulfonic acid, aralkylsulfonic acid, or a combination
thereof. The emulsion breaker can include alkylbenzenesulfonic acid
or dodecylbenzenesulfonic acid. The emulsion breaker can be admixed
at a rate of from 0.5 to 5 parts by weight per 100 parts of
substrate. The method can include recovering vapor generated from
the first mixing still, condensing the recovered vapor, and
exhausting non-condensed gases.
[0025] The method can further include continuously introducing the
treated solid substrate from the first mixing still into an inlet
end of a second mixing still which can include at least one shaft
disposed longitudinally in a housing and having a plurality of
impellors spaced along the shaft; continuously introducing a second
steam source into the second mixing still at a location adjacent an
outlet end thereof; and rotating the at least one shaft of the
second mixing still to maintain high shear conditions in the second
mixing still and continuously discharge a solid substrate from the
outlet end of the second mixing still, wherein the solid substrate
is essentially free of oil.
[0026] The method can also include peptizing the substrate with
alkaline earth, which can include lime. The alkaline earth can be
added to the substrate prior to being introduced into the first
mixing still. The method can further include peptizing the
substrate with mineral acid. The emulsion breaker can be admixed at
a rate of from 1 to 1.5 parts by weight per 100 parts of drill
cuttings. The method can further include recovering vapor generated
from the first and second mixing stills, scrubbing the recovered
vapor and exhausting non-condensed gases from the recovered vapor
into the atmosphere. The vapor can exit the mixing still through
insulated columns connected to a condensing column. The water
recovered by condensation can be recycled to the steam supply. The
substrate in the second mixing still can be fluidized.
[0027] In another embodiment is provided a method for treating
drill cuttings contaminated with oil. The method can include the
steps of: (a) continuously introducing the drill cuttings into an
inlet end of a first mixing still comprising at least one rotatable
shaft disposed longitudinally in a housing and having a plurality
of impellors spaced along the shaft; (b) continuously introducing a
first steam source into the first mixing still from a location
adjacent an outlet end thereof; (c) rotating the at least one shaft
of the first mixing still to continuously maintain high shear
conditions in the first mixing still and discharge an intermediate
solid substrate; (d) continuously introducing the intermediate
solid substrate into an inlet end of a second mixing still
comprising at least one shaft disposed longitudinally in a housing
and having a plurality of impellors spaced along the shaft; (e)
continuously introducing a second steam source into the second
mixing still at a location adjacent an outlet end thereof; (f)
rotating the at least one shaft of the second mixing still to
maintain high shear conditions in the second mixing still and
continuously discharge a solid substrate from the outlet end of the
second mixing still, wherein the solid substrate contains less than
3000 ppm oil; (g) recovering vapor from the first and second mixing
stills; and (h) condensing liquid from the recovered vapor to form
an exhaust stream of uncondensed vapor. The impellers on the first
and the second mixing still shafts are rotated at between 2 and 8
meters per second.
[0028] In another embodiment of the invention, an apparatus for the
treatment of an oil contaminated substrate is provided. The
apparatus can include means for admixing the substrate with steam
and agitation to vaporize the oil therein; means for recovering
steam vaporized oil; and means for recovering a treated substrate
of reduced oil content.
[0029] In another embodiment of the invention, an apparatus for the
treatment of an oil contaminated substrate is provided. The
apparatus can include means for pre-treating the substrate with an
organic emulsion breaker; means for heating the pretreated
substrate with a heat transfer medium to vaporize the oil; means
for recovering the vaporized oil; and means for recovering a
treated substrate of reduced oil content.
[0030] In another embodiment of the invention, an apparatus for the
treatment of an oil contaminated substrate is provided. The
apparatus includes: a first reactor comprising a longitudinal
housing having an inlet at a first end and an outlet at an opposite
end, the first reactor having at least one rotatable shaft disposed
longitudinally in the housing, and having a plurality of impellers
spaced along the at least one shaft; a second reactor comprising a
longitudinal housing having an inlet at a first end and an outlet
at an opposite end, the second reactor having at least one
rotatable shaft disposed longitudinally in the housing, and having
a plurality of impellers spaced along the at least one shaft; a
steam source for continuously introducing steam into the first
reactor at a location adjacent an outlet of the first reactor and
into the second reactor at a location adjacent an outlet of the
second reactor; a first feeder for continuously introducing the
substrate into the inlet of the first reactor; a chute for
continuously transferring reaction product from the outlet of the
first reactor into the inlet of the second reactor; a second chute
for continuously removing reaction product away from an outlet of
the second reactor; a vapor collection system for recovering gases
from the first and second reactors; a condenser for condensing
liquid from the gases from the vapor collection system and
producing a stream of uncondensed gases; and an exhaust port for
discharging uncondensed gases.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a process diagram for the treatment of oil-based
drill cuttings according to an embodiment of the invention.
[0032] FIG. 2 is a schematic overview of the apparatus according to
one embodiment, showing the primary equipment.
[0033] FIG. 3A shows a perspective view of one of the mixing still
housings according to one embodiment.
[0034] FIG. 3B schematically shows the horizontal flow pattern
inside the mixing still housing of FIG. 3A.
[0035] FIG. 3C shows the motion of the shaft and the vertical flow
patterns inside the mixing still housing of FIG. 3B.
[0036] FIG. 4 shows an elevation of the equipment according to one
embodiment of the present invention.
[0037] FIG. 5 shows another elevation for the equipment according
to another embodiment of the present invention.
DETAILED DESCRIPTION
[0038] The present invention provides a method and apparatus for
the thermal treatment of contaminated substrates with agitation for
the removal of volatile contaminants to produce a treated substrate
suitable for disposal. The process steps applied within this
invention include the sequential mixing of an oil-contaminated
substrate with a heat source with agitation. Preferably the heat is
supplied by the direct application of steam. Alternatively,
superheated steam can be supplied to vaporize the organic
contaminants. The application of heat initiates steam distillation
of oil and any other volatile organic contaminants present in the
substrate. The presence of water in the mixture can facilitate the
distillation and aid in vaporization of the volatile materials
being removed. Steam distillation is preferable to effectively
lower the distillation temperature of high boiling organic
compounds that are essentially immiscible in water. In these cases,
both the contaminant organic compound and the water exert their
full vapor pressure to establish an equilibrium between the
component partial pressures based upon temperature to the mixture.
The total pressure exerted by a mixture of immiscible liquids is
the sum of the vapor pressures of the individual components, at the
existing temperature. When the vapor pressure equals the total
pressure, the mixture will boil and the boiling point must be lower
than the vapor pressure of any of the components individually. The
result is that distillation of the higher boiling compounds can be
accomplished at much lower temperature than normally required. The
treated product can be a dried solid essentially free of oil and
other contaminants.
[0039] Alternatively, the oil-contaminated substrate can be
introduced into an aqueous environment and directly heated under
pressure and mixed with agitation to volatize any contaminates
present in the substrate. Preferably, the mixing can be under high
shear conditions. The oil contaminated substrate can preferably be
drill cuttings, containing a minor portion of oil by weight.
Preferably, the contaminated substrate contains less than 15
percent oil by weight, and more preferably less than 10 percent oil
by weight.
[0040] Drilling mud can be a stable emulsion comprised of several
chemical products performing many different functions for the
drilling of a well, such as temporary casing by the formation of a
filter cake, drill bit lubrication and cooling, as well as
facilitating removal of cuttings from the bottom to the wellbore.
The density of the mud can vary anywhere from between 900 g/l to 5
kg/l; however, all of the mud constituents must remain in
suspension during operation. During normal subsurface drilling
operations, drilling mud and cuttings from the different geological
strata are received at the surface for separation and recycling of
the mud. Drill cuttings can be clean as they exist in the
formation, but both at the drill bit and as they travel on their
way to the surface, the cuttings typically become contaminated with
the constituents of the mud. After separation of the mud from the
drill cuttings, the mud can be recovered for further reuse and the
drill cuttings must be disposed of.
[0041] The separation of the cuttings from the mud is not perfect,
as some mud remains within the cuttings, intimately mixed,
emulsified and often at high concentrations of the viscous
products, making the cuttings a viscoelastic product. In the same
cuttings, the chemical products can be bound up as contaminants,
forming a sticky matrix, which is difficult to handle and process
for decontamination. Thus, drill cuttings can present a very unique
technological problem for treatment since the matrix covering the
cuttings impedes the penetration of traditional treatment reagents.
These residues are not liquid, but are instead very stable
solid-liquid dispersions. The solid phase can be colloidal with
thixotropic properties, and the liquid phase can be an oil/water
mixture.
[0042] Although the present invention is described herein with
specific reference to drill cuttings as one example, and especially
drill cuttings obtained from operations with oil-based drilling
muds, other contaminated or environmentally hazardous wastes or
substrates can also be treated using the present methodology and
apparatus, especially clay-containing wastes. Drill cuttings can
contain large quantities of clay because the oil deposits and other
strata typically have a high content of clay. There are also a wide
range of applications for clay at the industrial level, such as in
ceramics, paper, drilling fluids, and certain types of lubricating
oils. Furthermore, clay can be used in insecticides, adhesives,
rubber and plastics, as a catalyst, or as catalyst support.
[0043] The present invention utilizes volatilazation and/or
chemical oxidation of contaminants to reduce contaminant levels
below those required for safe environmental disposal. The apparatus
is designed so that the process can be carried out in an automated
manner, continuously, reliably and efficiently. Energy usage per
treated weight unit of substrate is minimal. Following treatment
according to this invention, the treated drill cuttings or other
solid waste can be disposed of in any land fill as would any other
nontoxic, non-hazardous industrial residue.
[0044] Contaminated oil-based drill cuttings can be in the form of
a stable emulsion that must be broken before attempting treatment
of the drill cuttings. Breaking the matrix of the oil-based drill
cuttings is both a physical and chemical process, consisting of
taking apart and separating each one of the components, invariably
producing two liquid phases, an organic (oil) phase and an aqueous
phase, and a solids phase. The two phases can be formed by
modifying the polarity of each of the two phases within an aqueous
media through the addition of an emulsion breaker, which can be
enhanced by the addition of heat or agitation, or a combination
thereof.
[0045] The emulsion breaker can be an acidic or polyvalent compound
that is capable of destroying or "breaking" a water-in-oil
emulsion. Some emulsions associated with drilling cuttings can be
easily broken by a strong mineral acid, particularly where the
drill cuttings have a relatively high water content (>20
percent), low oil content (<30 percent), and are generally free
of large clumps or balls of solids. Other emulsions having a
relatively low water content or a relatively high oil content, or
that exhibit solids clumping, are not as easily broken by the
mineral acid alone and often require an additional emulsion
breaker. Alkylaromatic sulfonic acids, such as for example,
dodecylbenzenesulfonic acid (DDBSA), are materials that can change
the polarity of the solution and certain other physical properties
such as viscosity and interfacial surface tension, without
significantly altering chemical properties other than the pH. These
compounds can be used in relatively small volumes and can
preferably be biodegradable or chemically oxidizable without toxic
residue for use in environmental projects. In the present
invention, the emulsion breaker can preferably be an amphiphilic
molecule or ion, meaning that one portion of the molecule is
hydrophobic (water repellent) and another portion is hydrophilic
(attracts water). The hydrophobic (tail) portion is usually a
water-insoluble hydrocarbon chain, especially one of 12 or more
carbon atoms. The hydrophilic (head) portion is ionic or polar
water-soluble group (such as for example, oxyethylene chain,
--NH.sub.2, --SO.sub.2OH, etc.). Within the solution, the emulsion
breaker tends to concentrate at the water/oil interface, where the
hydrophilic heads can be hydrated with water, and the hydrophobic
tails are attracted to the oil molecules.
[0046] The demulsification can be done in two different manners, in
situ or ex situ. In situ demulsufication can be done by adding the
demulsifier directly to the substrate in the mixing still. Ex situ
demulsification can be done by adding the demulsifier to the
aqueous substrate prior to feeding the drill cuttings to the mixing
still, such as for example, adding the demulsifier to the substrate
in an open space on the drilling site or at a remote location. The
principles of in situ and ex situ demulsificaiton are generally the
same and predominantly depend on the demulsifier properties. Due to
the specific characteristics of each compound in both the drill
cuttings and the mud, different treatments are required so that a
generalization of the treatment process is difficult. Some of the
variables that can be controlled in breaking the emulsion include:
(1) type and quantity of demulsifier; (2) pH of the mix; (3)
quantity of transfer vehicle (e.g. water); (4) homogenization time;
(5) residence time; and (6) temperature of mixture. The
effectiveness of the technique can also depend on the
characteristics of the contaminated matrix of the cuttings, such
as: (1) permeability; (2) porosity; (3) homogenity of the medium;
(4) texture; and (5) mineralogy.
[0047] Although the temperature of the mixture can be an important
factor in breaking the organic phase, there are demulsifiers, such
as alkylbenzenesulfonates, preferably in acid form, i.e.
alkylbenzenesulfonic acids, such as for example, dodecylbenzene
sulfonic acid (DDBSA), that work at ambient temperature. Use of the
demulsifier at room temperature facilitates treatment and
safeguards the operation, thereby eliminating the need for external
heating and lowering the overall treatment costs. Either linear or
branched alkylbenzenesulfonic acids can be used advantageously to
break the emulsion.
[0048] Preferably, the addition of the demulsifier results in
essentially complete breaking of the emulsification without
requiring the addition of excess demulsifier. Excess demulsifier
often requires the addition of alkaline earth, as described below,
and increases the overall cost of the process. In most
applications, the proportion of emulsion breaker employed can range
from 0.5 to 5 parts by weight per 100 parts of substrate (pph),
preferably from 1 to 3 pph, and especially from about 1 to about
1.5 pph. The pH of the raw drill cutting can also affect the amount
of DDBSA required to break the emulsion. For example, if the pH is
relatively low (for example 9), the optimum quantity of DDBSA may
be 1 pph, but when the pH of the matrix is relatively high (for
example 13), the optimum quantity of DDBSA might be 1.5 pph.
[0049] The emulsion breaker can be added as a neat liquid or as a
solid, but it is most conveniently added as a liquid. Depending on
its physical state at ambient temperature, the emulsion breaker may
need to be liquefied by heating and/or by dilution with water or
other solvent. In this manner, the water required for the
distillation process can be conveniently added with the emulsion
breaker, in amounts described below. For example, the emulsion
breaker can be added to the raw drill cuttings from an aqueous
solution typically containing from 5 to 10 weight percent of the
DDBSA.
[0050] As previously mentioned, the invention can be particularly
applicable to hazardous wastes containing clay. When clay contacts
organic compounds and water, its physical-chemical behavior can be
altered, often causing unpredictable results. These changes can be
reflected in the formulation of extremely stable dispersions, which
become more stable when in water or soil, where chemical compounds
which form ions in aqueous solution can be found.
[0051] The treatment of the contaminated substrate can be
facilitated by the initial treatment with DDBSA, especially where
the drill cutting matrix is very sticky, as is the case in high
oil/low water mixtures. The subsequent treatment of the high
oil/low water mixtures with mineral acid and/or alkaline earth is
efficient and economical, without compromising the environment. The
mixture can be peptized, thereby forming a colloidal suspension to
better separate the components for exposure to the steam. Peptizing
is a physical process that does not break the molecules, and does
not flocculate the components of the mixture. In this process,
chrome salts, manganese and iron are preferably avoided. During the
acidification, apart from destabilizing the agglomerated clay
particles, the solid phase is activated to develop its colloidal
properties and promote peptization. The peptization can occur to an
even greater extent upon the addition of lime. The addition of
acid, or more preferably alkaline earth, can facilitate peptization
and ensure that the substrate particles are sufficiently small
enough to allow for suspension of the particles in the air when
subjected to high shear conditions. The suspension of the particles
facilitates proper contact between the contaminated substrate and
the steam, allowing for short residence times in the mixing still,
and rapid distillation of the volatile organics from the
substrate.
[0052] The use of steam as a method of supplying direct heat for
the decontamination of contaminated substrate replaces the need for
the storage and application of large volumes of highly caustic
substances such as concentrated mineral acids. Preferably the steam
is applied under low pressure. Additionally, under certain
circumstances, steam may be more readily available and less
expensive than the alternate heating or decontamination sources.
Steam may be produced by any conventional method, and can be
introduced to the mixing still at a pressure of between 70 and 350
KPa (10 and 50 psi), preferably between 140 and 280 KPa (20 and 40
psi), and more preferably, at approximately 210 KPa (30 psi). For
most applications, steam is preferably continuously introduced to
the mixing still at a rate of at least 20 kilograms of steam per
kilogram of oil in the substrate, depending on the concentration of
the contaminant in the substrate. In addition, external heat can be
applied indirectly to the large mixing still wherein the substrate
or contaminated material is contained in an aqueous solution, or
direct heat can be supplied through the addition of hot air or hot
nitrogen, at a rate of at least 1 kilogram of air per kilogram of
oil in the substrate, to the mixing still system. Ideally,
sufficient steam and/or heat can be applied to ensure that the
steam and volatilized hydrocarbons do not condense to form a liquid
in the mixer. The addition of hot air and/or hot nitrogen can also
assist in keeping the steam and hydrocarbons in the vapor
phase.
[0053] Due to the temperatures generated by the application of
steam to the substrate, much of the water present in the drill
cuttings, and much of the water added to the drill cuttings with
the emulsion breaker, may be vaporized. If too much water is
initially present in the mixture, taking into account the water
present in the drill cuttings, the reaction temperature may be
suppressed to the point that the volatilization of the organics and
water can be adversely affected, and the end product may contain an
undesirably high level of moisture and/or non-volatilized
hydrocarbons. On the other hand, if too little water is added, the
emulsion may not be adequately broken, and the substrate and the
treated product may be too dry, thereby causing dusting.
Furthermore, if the emulsion is not adequately broken, the
hydrocarbons may not be exposed to the steam and may remain within
the treated mixture. As a practical matter, the quantity of water
added with the emulsion breaker, for example, can be adjusted until
the desired amount of steam per kilogram of oil is reached for
optimum conditioning of the substrate. The water is preferably
added with the emulsion breaker, but can also be added separately.
The proportion of water in the drill cuttings following emulsion
breaker addition is preferably in the range of from 20 to 40 pph.
Alternatively, the emulsion breaker can be preheated to reduce the
temperature of the steam and/or hot gas added to the mixing
still.
[0054] The alkaline earth is preferably lime and can be added in
amounts determined by the pH and type of substrate. Generally,
substrates having a pH less than 10 require the addition of greater
amount of alkaline earth. In addition, when the substrate materials
include hard shale and clay, the substrate may require the
application of alkaline earth to pre-treat the substrate prior to
steam distillation. Sands generally do not require pretreatment
with an alkaline earth. However, not every steam distillation
process requires the addition of alkaline earth. A variety of
factors, including the pH of the drilling fluid and the clay
content of the substrate, determine whether the addition of
alkaline earth is necessary. The alkaline earth typically
conditions the substrate, reducing it into small particles. The
smaller particle size allows the particles to become suspended in
the steam when subjected to agitation, or more preferably to high
shear conditions, resulting in more effective contact between the
steam and the substrate and a more effective distillation. If
desired, lime can be added to the substrate prior to introduction
into the first mixing still, directly into the first mixing still
for admixing with the substrate, or directly into the second mixing
still, when a second still is employed.
[0055] The amount of alkaline earth added to the substrate varies
from case to case, generally depending upon the amount of
hydrocarbon present in the substrate. When necessary, lime can be
added in an amount of between 5 and 25 percent by weight of drill
cuttings, preferably from 8 to 15 percent by weight.
[0056] Material conditioning refers to the maximum moisture content
present in the treated solid at the end of the process, and is
preferably not less than 3 weight percent so that handling and
final disposition are facilitated. The conditioning of the treated
solid is another advantage of the present invention because the
initial product has a relatively high moisture content as compared
with the finished product, which is an easily handled dry powder,
thereby allowing for final disposal of the treated solids without
water as a significant residue. The specific gravity of typical oil
based drill cuttings can be transformed, for example, from
approximately 2.2 at the input to between 1.1 and 1.2 in the
treated cuttings. In the present process, the water content of the
treated solids can be controlled to avoid dusting while at the same
time maintaining a low water content and avoiding the need for any
post-treatment processing such as spraying the treated solids with
water or a surfactant, as can be necessary in some prior art
processes.
[0057] FIG. 1 shows a flow diagram of the treatment of oil-based
drill cuttings, indicating the different steps of the distillation
process. Drill cuttings 10 are supplied to mixing still 12, where
they can combine with heat, preferably applied as steam 16, and
optionally an emulsion breaker 14, and can be mixed under high
shear conditions. The mixing still 12 can be insulated, heated
electrically, or jacketed with steam or other heat transfer fluid.
Optionally, an alkaline earth material 11, such as for example,
lime, can be added to the drill cuttings prior to addition to the
first mixing still. The partially treated drill cuttings from
mixing still 12 can be introduced into a second mixing still 18,
which can be insulated and/or heated, as previously described with
respect to the first still, where an optional second source of
steam 20 can be added. The treated cuttings 22 can be discharged
from mixing still 18 and can be taken to their final disposal. The
steam applied to the substrate can be sufficient to volatize the
oil, as well as other volatile organic compounds, by low pressure
steam distillation. These gases pass through a vapor collection
system and condenser 24 to collect the condensate 28. The
non-condensed gases 26 can be vented to the atmosphere. If desired,
the condensate 28 from vapor collection/condensation 24 can be
separated into oil 30 and water 32 phases. The water phase can be
recycled and used to dilute the demulsifier 14, provide water for
the steam sources 16 or 20, or as needed for control for the
moisture content in the treated cuttings 22.
[0058] FIG. 2 shows the process and the main equipment involved in
one embodiment of the invention. The cuttings can be supplied to
the system from the cuttings chute 100 and flow by gravity to the
cuttings dosage feeder 102. The cuttings can be discharged by
gravity to an inclined drag conveyor 104. The untreated cuttings
can be raised to the height necessary to be discharged into the
first mixing still 106. The first mixing still 106 preferably
includes a vapor lock or rotary injector 105 to inhibit the entry
of air. Optionally, lime from feeding hopper 119 may be added,
dosing through feeder 120, to the cuttings chute 100 for
pretreatment of the contaminated substrate prior to introduction to
the first mixing still 106. In mixing still 106, a demulsifier can
be added from storage tank 108, fed through automatic dosage pump
112. Steam can be added from steam supply 110 via valve 114, in
proportion to the quantity of drill cuttings.
[0059] Inside the first mixing still 106, any sticky component
covering the matrix of the drill cuttings is broken away by the
demulsifier and vigorous mixing conditions, exposing the components
of the cuttings to the steam, which occurs continuously within the
still 106. The materials and design of mixing still 106 help to
inhibit sticking of the drill cuttings to the walls and moving
parts, although there is no serious detriment to such solids
buildup and perhaps may provide some insulating effect. The
inhibition of solids sticking is achieved through the use of metal
alloys, as well as through the high tangential speeds of the moving
parts and the drill cuttings. Once the matrix has been broken and
the substrate has been heated or steam treated, the modified matrix
can be discharged by gravity via chute 116 into the second mixing
still 118.
[0060] Inside the second mixing still 118, a second source of heat,
preferably applied as steam, can be added from steam supply 110,
controlling the addition through valve 113. The second mixing still
118 similarly prevents the buildup of solids as described above
with respect to the first mixing still 106. The decontaminated
cuttings pass through valve 121 and are emptied onto the inclined
transport belt 124 and discharged by gravity into the dump trucks
126 or other disposal receptacle. The valve 121 is preferably a
rotary valve or other valve providing a vapor lock inhibiting the
entrance of air into the still 118. The decontaminated cuttings may
be further treated to reduce the pH if necessary. Removal of gases
from the first or second mixing stills 116, 118 can be facilitated
by induced draft fan 128, which can remove the gases produced in
stills 106 and 118 through discharge connections 115 and 117
respectively, and supplies the vapors to the condensation column
130. Connections 115 and 117 are preferably insulated to prevent
premature condensation of the steam and hydrocarbon gases.
Optionally, hot air or hot nitrogen gas, supplied at approximately
200.degree. C. (400.degree. F.), can be introduced to either one or
both of the mixing stills through an inlet (not shown) located near
the outlet end of the mixing still. The counter-current addition of
hot gas can facilitate both the hydrocarbon vaporization and also
provides a current for removal of the water and hydrocarbon vapor.
The non-condensed gases (primarily air and CO.sub.2) can be vented
to the atmosphere via line 131. The condensation column 130 can be
an indirect heat exchanger that cools the gases to form condensate.
Alternatively, the condensation column 130 can employ an absorbent,
such as for example, water or a commercially available caustic or
amine solution, and provide direct heat exchange by contacting the
gases with the cooled circulating absorbent. A coolant circulation
pump 132, heat exchanger 134 and collection/settling drum 136 can
be used to facilitate vapor condensation. Water separated from the
condensed gases may be recycled to the steam production 110 (not
shown), or added to the demulsifier as a diluent. Accumulated
immiscible liquid such as oil or heavy hydrocarbons can be
periodically or continuously removed from the drum 136 via line
138. The heat exchanger 134 can be cooled by air or water or any
other conventional cooling medium.
[0061] FIG. 3A shows a perspective view of a housing for mixing
still 200, which can be used for either of the mixing stills 106,
118, which can have the same general dimensions and construction.
FIGS. 3B and 3C, respectively, show a schematic plan view of the
movement of material in mixing still 200, and a schematic elevation
of the movement of material in the still 200. Mixing still 200 can
include a housing 202, an inlet opening 204 in an upper surface at
one end of the mixing still 200, an exhaust vent in an upper
surface adjacent inlet opening 204, a discharge opening 206 in a
lower surface at the other end of the mixing still 200, and a steam
inlet 203 in the lower surface adjacent discharge opening. A pair
of shafts 208 are longitudinally aligned in the housing 202 and can
be rotated in opposite or complementary directions. A plurality of
impellers 210 in the form of pins can be positioned along the
length of the shafts 208. The impellers can be ideally pitched to
facilitate maximum shear conditions for agitation and movement of
the solids, preferably between 70.degree. and 85.degree., more
preferably between 75.degree. and 80.degree.. The arrows in FIGS.
3B and 3C show the horizontal and vertical direction of the
movement of the materials, as dosed, including the oil-based drill
cuttings and the three reagents. If desired, baffles (not shown)
may be positioned between adjacent impellers 210. The internal
design and construction materials for the mixing stills are
preferably such as to resist extreme pH environments within the
process when the heat is provided through the addition of a mineral
acid and alkaline earth source, e.g. stainless steel alloy. The
substrate and the reagents preferably follow three different
movements simultaneously: (1) circular motion on the vertical
plane; (2) linear-transverse motion (U type); and (3) longitudinal
linear motion along the mixing stills, allowing for the input and
output volumes and speeds to be the same.
[0062] The speed of the materials throughput, as well as the
specific materials used to manufacture the mixers 106, 118, prevent
the viscoelastic hydrocarbon and cuttings matrix from sticking to
the walls of mixer 106. The moving speed at the tip of the
impellers 210 ideally can be between 2 and 8 m/s (7 and 26 ft/s) on
rotation and approximately 0.2 m/s (0.7 ft/s) on the translation in
both directions (U and linear). More preferably, the tip speed is
between 2 and 5 m/s (7 and 16 ft/s), and especially between 2.5 and
3.5 m/s (8 and 12 ft/s). As one example for a mixer treating 10
metric tons per hour of drill cuttings (5 m.sup.3/h or 180
ft.sup.3/h), the mixers 106, 118 can each have twin parallel shafts
approximately 3 m (10 ft) long, running the length of the mixer,
each with at least 30 paddles/shaft and a 0.4 m (1.3 ft) diameter.
The total residence time preferably does not exceed between 100-120
seconds inside the two mixers (i.e. between 50-60 seconds in each
mixer), more preferably the total residence time preferably does
not exceed between 80-100 seconds inside the two mixers (i.e.
between 40-50 seconds in each mixer). The speed of impeller 210 is
critical in creating favorable conditions for the distillation of
the substrate contaminants. If the impeller speed is too slow, the
substrate will not be properly suspended in the mixer, resulting in
poor contact between the contaminated particles and the steam. If
the speed of the impeller is too fast, energy is wasted as no
improvement in reaction conditions or suspension of the substrate
is achieved.
[0063] The distillation process requires vigorous agitation of the
cuttings within the mixing stills. Preferably, high shear
conditions are maintained in the mixing stills, i.e. sufficient
agitation to maintain the substrate in a fluidized condition and to
avoid formation of dense phase accumulation other than minor caking
on interior mixer surfaces. The energy for agitation preferably
should not exceed 1.5 hp per metric ton of treated substrate per
hour. For example, to treat 30 metric tons per hour of contaminated
drill cuttings, the total power required is preferably less than 45
hp. This process can take place at a pressure slightly above
atmospheric, thus, a pressure vessel is not required. Preferably,
the distillation takes place at a pressure slightly lower than
atmospheric pressure. The materials of construction of the mixing
still 200 internals are preferably a high nickel stainless steel
alloy resistant to corrosion at the pH extremes and the
temperatures experienced.
[0064] In one embodiment of the present invention, a treatment
method is provided for offshore applications where the footprint
available for the apparatus is limited and generally smaller than
what is available in a land based treatment process. To operate
under these circumstances and meet the small footprint
requirements, the mixers can be positioned in a different
alignment, such as for example, the first and second still can be
arranged in a vertical alignment rather than a horizontal
alignment. The horizontal lay out typical for land-based treatment
of contaminated substrates is shown in FIG. 4, while the vertical
arrangement more typical for offshore platforms and other
applications requiring a minimum footprint size is shown in FIG. 5.
For example, in FIG. 5, the second mixer 118 is located directly
beneath the first mixer 106.
[0065] The solids feeders 140 and 144 in FIG. 5 are preferably
rotary feeders to create an air lock to inhibit the entry of air
into the mixers 106, 118, which might otherwise tend to reduce the
mixer temperature. Alternatively, a spring-biased damper (not
shown) can be used to inhibit air entry into the system.
[0066] The equipment can be installed permanently or in portable
units or modules for temporary applications. If desired, the units
can be mounted to wheeled bases for ease in transporting to and
from different job sites. In addition to the mixers, other
peripheral or secondary equipment is needed as per the handling and
metering out of materials handled. This equipment can include
hoppers, tanks, feed-meters, pumps and conveyors of different
types, in addition to control equipment. The process can be
continuous so as to achieve maximum equipment efficiency, lower
energy consumption and lower production costs. The process can be
automatic so as to insure consistency and unitary process
control.
EXAMPLE
[0067] A test of the process and apparatus is conducted to treat
drill cuttings contaminated with an oil-based drilling mud. The
cuttings have an oil content of approximately 13% and a pH of
approximately 11.0. The cuttings are supplied at ambient
temperature and are continuously processed at a rate of 900 kg/h
(2000 lb/h) (15 kg/min; 30 lb/min) two mixing stills arranged in
series, each having a capacity of approximately 200 liters (40
gal), twin parallel shafts approximately 2 m (5 ft) in length with
25 paddles/shaft and a 0.2 m (0.7 ft) diameter and a tip speed of
at least 3 m/s (7 ft/s). The average residence time of the cuttings
in each mixing still is approximately 80 seconds. Steam is
continuously added at approximately 30 psi (200 KPa) to an inlet
adjacent the outlet of the first mixing still at a rate of 2 kg/min
(4 lb/min), and the temperature in the first mixing still is
maintained at greater than 100.degree. C. (212.degree. F.) near the
outlet. A second steam source is continuously introduced to the
second mixing still, adjacent the outlet of said second mixing
still, at a rate of 2 kg/min (4 lb/min), and the outlet temperature
of the second mixing still is maintained at greater than
100.degree. C. (212.degree. F.). After establishing steady state
operation, treated drill cuttings are recovered from the solids
discharge at a rate of 20 kg/min (40 lb/min) and have a solids
content of approximately 85 weight percent, a hydrocarbon content
of less than 3000 ppm, a water content of approximately 3 weight
percent, and are in the form of a non-dusting powder. Vapor is
recovered from a location adjacent the inlet of the first and
second mixing stills using an induced draft fan at a rate of 150
kg/min (300 lb/min), comprising approximately 25 weight percent
hydrocarbons, and approximately 75 weight percent steam. The vapor
is cooled to condense and recover 2 kg/min (4 lb/min) of
hydrocarbon material, 2 kg/min (4 lb/min) of water; and 7 kg/min
(15 lb/min) of uncondensed vapor are vented when hot air is
added.
* * * * *